Magnavox astro sonic twitter speaker replacement

For what it's worth, it's not always about "replacing the caps".
That so-called idea has run rampant across the internet for years.
"change the caps! - change the caps!"

It's not the golden "fix" in many cases, sorry.

Electronics is a vast ocean of technology, and a good technician does more than "change the caps"...
There's also resistance readings, among other things.
There's dynamic testing involving voltage checks, bias readings, and waveform patterns.
Adjustments sometimes have to be made, alignment procedures to follow, etc.

So any so-called "tech" that just "changes caps", I have to wonder about their competence level.

"spierce10"

I held off responding till I had time to find one of those "tweeters" here.

Bobby is correct, they are essentially midranges with some treble response.

I have a 1965 Magnavox console and when I rebuilt it in Jan. 1990 I did note the recessive highs.

If you look at Mr Basham's pic of the crossover you will see two light grey brick shaped resistors. These reduce the output of the tweeters.

I tested one of those I have on-hand here and it measures 11.9 ohm DC. That means it is approx a 16 ohm speaker. The resistor is rated at 10 ohms. This means that close to three decibels are being attenuated with it in series with the tweeter. The attenuation of the highs may be slightly more due to the fact that the resistor in not non-inductive.

You may get somewhat more treble by bridging out that resistor. This will also raise the crossover frequency and it will be necessary to increase the size of the 8mfd capacitor to completely restore the original crossover points. But -carefully-try it anyway.

If you feel competent at reading schematics, this is the speaker setup of my machine, and probably yours too:

http://www.fileconvoy.com/dfl.php?id=gb ... 6e888ab612 Rename the extension to .jpg I don't know why Fileconvoy renames them.

The area of interest in the lower right hand side. Note; the connection to the machine speaker switch is WRONG (it would place the two sides in series) but the crossover components directly connected to the speakers are correctly shown.

From an aesthetic standpoint, these machines were intended for a market where a "plush" -bassy sound was desirable. The phono pickup input was given some additional high filtering to suppress distortion from record wear.

On my machine I changed the pickup to a magnetic and added a preamp. That may be further than you are willing to go, but it does improve the sound and lowers the tracking distortion radically.

How does the radio tuner sound?

I have a full set of schematics that are probably applicable for your model. I'll send you links if you P-M.

Rob/NYC

Rob,
The link you posted has expired. I was interested in where you say the diagram is wrong. I'm having trouble getting both channels to work but everything looks right. Thought this might have something to do with it. Thanks.

Rebaisden wrote:Rob,
The link you posted has expired. I was interested in where you say the diagram is wrong. I'm having trouble getting both channels to work but everything looks right. Thought this might have something to do with it. Thanks.

I have found that when both channels don't work, it's due to dirty controls. It's not uncommon to find a defective cartridge which could be the cause of "one-sided" issues, so check your unit in the radio and aux modes to see if the problem persists. If so, any of those rotary selector, balance bass, treble, volume controls etc., will affect the channels. I've had to rock all of them back and forth to bring both channels into play. The chassis needs to be removed and serviced. Those controls need to be sprayed with some type of cleaner and lubricant, like Deoxit. If that still doesn't work, then there are other things going on. Replacing caps is not a "Fix-all" for all the issues. I've also come across resistors on the chassis choking the audio chain. Components are labeled, but it helps to have a schematic to verify voltages and other interesting tidbits you find in them. Find a good tech if you can't handle this yourself. --BB

Bobby Basham
Tucson, Arizona